33 Non-destructive Measurement of Retained Austenite Content in Austempered Ductile Iron Yoshio Kato, Sen-ichi Yamada, Takayuki Kato, Takeshi Uno Austempered Ductile Iron (ADI) 100kg/mm 2 10 ADI 10 X ADI Abstract Austempered ductile iron (ADI) is noted for its combination of high strength and wear resistance. In recent years, much attention has been paid to ADI as a prominent material for reducing weights and costs of automobile components. Usually, ADI shows poor machinability, due to strain-induced transformation of the retained austenite. If it is possible to measure the amount of retained austenite before machining, we can prevent the chipping of cutting tools. For measurement of the amount of retained austenite, X-ray diffraction is the only method capable of giving an absolute value, but it can not be applied to the non-destructive quantitative analysis of castings. However, we found a strong relationship between the amount of retained austenite and the induced voltage in the AC magnetization method. A retained austenite meter on the basis of this method is used for inspection of ADI rotors for automotive air conditioning compressors.
34 Austempered Ductile Iron ADI 100kg/mm 2 10 ADI Ms ADI 10 ADI ADI X X10µm ADI Fe-3.8% C-2.4% Si-0.26% Mn-0.008% S-0.023% P-0.04% Mg ( wt ) φ8 22mm 900 1h 375 450 0 40 5 10 TRF-5AH 10kOe Microstructures of ADI (27 retained austenite).
35 200Oe 1kOe 10kOe AC BH-100K 490mm 270mm 60Hz 500Hz 2kHz 10kHz 11mm 9mm 0.15mm 602 2 31mm 28mm 18mm 0.4mm 150 (a) (c) 200Oe 10kOe (a) (b) (c) 0 12 39 5kOe 10kOe 4π I 10k Schematic diagram of AC magnetization method. DC magnetization curves of ADI.
36 γ R mag. γ R mag. = 1 4π I 10k 1 G 4π I 10k 100 100 4π I 10K 10kOe G 10vol ) 10kOe 4π I 10K 500 1hr 17.2kG X X α Fe ( 200 ) ( 211 ) γ Fe 200 ) ( 220 ) ( 311 ) γ R Xray 6 γ R mag. 1:1 γ R mag. 1.04 γ R Xray 1.10 0.97 200Oe 1kOe 10kOe 0 39 30Oe 200Oe 1kOe 10kOe (a) (d) Fig. 1 0 12 39 (a) (b) 60Hz 500Hz 15Oe (c) 2kHz 6Oe (d) 10kHz 1Oe (a) 60Hz 15Oe 0 143G 12 134G 39 114G (b) 500Hz 60Hz 15Oe 0 128G 12 120G 39 102G 60Hz 10 (c) (d) Relationship between the amount of residual austenite by X-ray diffraction method and DC magnetization method. µ max Effect of the amount of retained austenite on DC magnetic properties of ADI.
E = 2 π N S 4π I f 10 5 E mv N 60 S mm 2 4π I G f Hz (a) (d) Fig. 5(a) (d) (b) (3) 60Hz 500Hz (a) (d) (a) (b) 60Hz 500Hz 15Oe (c) (d) 2kHz 6Oe 10kHz 1Oe Fig. 1 (a) (d) (a) (b) 60Hz 500Hz 15Oe (c) 2kHz 6Oe (d) 10kHz 1Oe (a) (d) (a) 60Hz 15 125Oe (b) AC magnetization curves of ADI. Induced voltage by AC magnetization method.
38 Relationship between the amount of retained austenite and induced voltage by AC magnetization method. Differential AC magnetization curves. (standard sample : γ R =0 ) 500Hz 15Oe (c) 2kHz 6Oe (d) 10kHz 1Oe (a) 60Hz (b) 500Hz 0.1A 0.5A 0.5A 26Oe 18Oe Fig. 3 Fig. 4 Fig. 9 Fig. 10
39 Relationship between the amount of retained austenite and differential induced voltage by AC magnetization method. Fig. 10 1/e ( =36.8 ) δ mm δ = 50.3 ρ / µ f Relationship between the amount of retained austenite and differential induced voltage by AC magnetization method with dual solenoid coils instead of helmholtz coil. ρ µω cm µ f Hz)
40 100µΩcm 100 ADI ADI 900 30 325 13mm 8mm φ8 20mm φ6 11mm 1 2 13mm 100Hz 200mA 78mm 70mm 0.45mm 180 Depth of penetration as a function of frequencies for ADI. Retained austenite meter for austempered ductile iron rotor. Specifications of retained austenite meter. Austempered ductile iron rotor for car air conditioning compressor.
41 8Oe 60mm 51mm 0.15mm 1000 Photo. 2 300mm γ R 0.17 E 1.8 0.99 γ R E mv ) Photo. 2 430 430 440 ADI ADI 1 5 6 60 70 Calibration curve between the amount of retained austenite and output voltage of retained austenite meter. Influence of austempering temperature on retained austenite content of ADI rotor.
42 ADI (1) ADI 30Oe 10kOe 4π I 10k kg γ R mag. X 1:1 γ R mag. = 1 4π I 10k 1 G 4π I 10k 100 100 4π I 10K 10kOe ( 17.2kG ) G 10vol ) (2) ADI ADI 100Hz 1, (1991), 215p. 2), :, -6(1991), 79 3,, :, -6(1989), 19 4 :, -1(1989), 7 5, :, -5(1987), 310 6 Harding, R. : 2nd Int. Conf. on ADI, ASM., USA, (1986), 39 7 Mayer, H. and Barbezat, B. :. 6), p.99 8, :, -8(1986), 1010 9 :, -12(1986), 823 10 :, -6(1984), 362 11,,,, : -9(1989), 620 12,,, :, No.19(1989), 21 13,, :, -3(1987), 147 14,, :, -9(1989), 615 15),,, : 21, (1988), 7 16), :, -7(1987), 396 17),,, :, -1 (1992), 16 18),, :, -11(1987), 658 19), :, -3(1990), 196 1946 1936 3 1993 4 ASM (American Society for Metals) 1944 1961